Epidemiologic studies of occupational groups are conducted to identify and clarify the role of environmental factors in the origin of cancer. Potential for heavy and prolonged exposure, coupled with the availability of work history records, make occupational groups invaluable for epidemiologic investigations of cancer. Numerous occupational groups are under investigation. Completed during the past year were studies of 1) pesticide applicators revealing an excess of lung cancer that rose with the number of years employed; 2) professional artists exposed to paints and solvents, revealing high frequencies of deaths from cancers of the bladder, kidney, brain, colorectum, prostate, and breast; 3) professional photographers likely to have contact with developing chemicals who had an increased frequency of deaths from pancreatic cancer; 4) farmers who had an elevated risk of multiple myeloma, particularly those who resided in counties where chicken inventories were high or where fertilizers and insecticides were more frequently used; 5) workers in the tobacco industry where the relative frequencies of various causes of death were not strikingly different from those seen in the general U.S. population; 6) textile workers where, unlike previous reports, the risk of prostate and colon cancer was not associated with employment in the textile industry; 7) the latent period of angiosarcoma of the liver that indicated cancers induced by vinyl chloride appear sooner after the initial exposure than cases caused by thorotrast; and 8) workers in oil refineries where a case-control study using complete work histories uncovered no striking associations between brain cancer and particular work categories. Other investigations underway include proportionate mortality studies of plumbers, foresters, and embalmers; cohort mortality studies of formaldehyde workers, anatomists, dry cleaners, furniture workers, shipyard workers, aircraft mechanics, potters, grain millers and handlers, and chemists; and case-control studies of leukemia, lymphoma, soft-tissue sarcoma, mesothelioma, colon polyps, and brain and lung cancer.